The present invention relates to a switching circuit and control method thereof; and more particularly, to a switching circuit and an electronic switching component having a switching semiconductor device to perform switching operation between a conducting state and a non-conducting state of a conducting path and a control method thereof.
Conventionally, a DC-to-DC converter is known in the art as a typical circuit in which a switching semiconductor device, e.g., a transistor or a field effect transistor (FET) is employed to have a direct current to flow intermittently, wherein this direct current is smoothed out by using a coil or a condenser to thereby output an output voltage different from a corresponding input voltage. This DC-to-DC converter is usually used in a conversion circuit which converts a voltage inputted thereto from a direct current source to a different voltage.
FIG. 2 shows a conventional DC-to-DC converter circuit 20. The conventional DC-to-DC converter circuit 20 includes a smoothing reaction circuit 22, a switching semiconductor device 23, a smoothing condenser 24, a commutating diode 25, a smoothing condenser 26 and a switching integrated circuit (IC) referred to as a control IC 27.
The switching semiconductor device 23 receives an input voltage Vin from an input terminal 21a and then outputs a corresponding output voltage Vout through the smoothing reaction circuit 22 to an output terminal 21b. The smoothing condenser 24 is connected between the output terminal 21b and a ground. The commutating diode 25 is connected to the circuit at a point between the smoothing reaction circuit 22 and the switching semiconductor device 23; and is connected to the smoothing reaction circuit 22 and the smoothing condenser 24 in parallel, wherein the commutating diode 25 is connected to the smoothing reaction circuit 22 with a polarity to maintain the current of the smoothing reaction circuit 22.
The smoothing condenser 26 is connected between the input terminal 21a and a ground. The control IC 27 monitors the voltage Vout outputted to the output terminal 21b and carries out ON-OFF controlling of the switching semiconductor device 23 to maintain the output voltage Vout at a constant value.
In the DC-to-DC converter circuit 20 as mentioned above, during ON state of the switching semiconductor 23, Vin inputted to the input terminal 23a is smoothed through the smoothing reaction circuit 22 and the smoothing condenser 24 so that a smoothed voltage is outputted through the output terminal 21b. During OFF state of the switching semiconductor 23, the current of the smoothing reaction circuit 22 is maintained by the commutating diode 25 in such a way that a constant voltage is outputted through the output terminal 21b. In this case, the control IC 27, in accordance with the change of the output voltage Vout, alters a pulse width of a pulse signal used in controlling ON-OFF operation of the switching semiconductor 23 to thereby perform a feedback control to maintain the output voltage Vout at a constant value.
But, in general, it takes time to switch between an ON-state and an OFF-state of a switching semiconductor device, e.g., a transistor or a FET. This time is usually referred to as a switching time. A switching loss increases as the switching time becomes longer. For example, during a change between the ON-state and OFF-state of the switching semiconductor 23, e.g., during a time interval between t(1) and t(2) as shown in FIG. 3, there entails a power loss of Vdsxc3x97Id, wherein Vds and Id are a drain to source voltage and a drain current, respectively.
Further, since there is usually an inverse proportional relationship between a switching speed from ON-state to OFF-state and vice versa and an ON-resistance (saturation resistance) of a switching semiconductor device, e.g., a transistor or a FET, it is impossible to realize both the increase of switching speed and decrease of ON-resistance simultaneously by using only one device. For this reason, in a conventional switching control method, a switching circuit is prepared by compromising between a switching speed and a ON-resistance (saturation resistance) of a switching semiconductor.
It is, therefore, a primary object of the present invention to provide a switching circuit and an electronic switching component having a switching semiconductor device to perform switching operation between a conducting state and a non-conducting state of a conducting path and a control method thereof.
To achieve the above-mentioned object of the present invention, the relationship between the switching speed (switching time) corresponding to an area of a switching semiconductor device and an ON-resistance (saturation voltage) thereof is employed to reduce the power loss thereof. For example, the ON-resistance may be an ON-resistance of a field effect transistor (FET) or an equivalent resistance corresponding to a saturation voltage of a transistor.
There is usually an inverse proportional relationship between a switching speed and an ON-resistance (saturation resistance) of a switching semiconductor device, e.g., a transistor or a FET. Namely, as the chip area of a switching semiconductor device increases, the ON-resistance (saturation voltage) decreases. Further, as the chip area of a switching semiconductor device increases, the capacitance thereof increases. Then the input/output signal wave becomes dull to thereby reduce the switching speed.
In accordance with one aspect of the present invention, there is provided, by employing the relationship between the switching speed and the magnitude of the ON-resistance (saturation voltage), a switching control method for connecting switching semiconductor devices to a conducting path and switching between a conducting state and a non-conducting state of the conducting path, the method comprising the steps of: (a) connecting active terminals of two or more switching semiconductor devices in parallel; and (b) switching between a conducting state and a non-conducting state of the conducting path by employing the two or more switching semiconductor devices.
In accordance with another aspect of the present invention, there is provided a switching circuit having switching semiconductor devices connected between an input terminal and an output terminal thereof for switching between a conducting state and a non-conducting state of a conducting path between the input terminal and the outout terminal thereof in response to a control signal inputted thereto from outside, the switching circuit comprises: two or more switching semiconductor devices connected in parallel to each other between the input terminal and the output terminal thereof; and a control circuit for controlling converting between conducting states and non-conducting states of the two or more switching semiconductor devices.
In accordance with yet another aspect of the present invention, there is provided an electronic switching component comprising: a package; two input/output outer terminals exposed from the package; two or more switching semiconductor devices formed in the package connected in parallel between the two input/output outer terminals, wherein at least one of the two or more switching semiconductor devices has switching property different from those of the outer switching semiconductor devices; and one or more outer control terminals connected to each of the switching semiconductor devices, wherein the one or more outer control terminals are exposed from the package.
In accordance with still another aspect of the present invention, there is provided an electronic switching control component for inputting an ON/OFF control signal and then outputting two or more device control signals for use in controlling two or more semiconductor devices in response to the ON/OFF control signal, the component comprising:
a package; a control signal input terminal exposed from the package for inputting the ON/OFF control signal; two or more device control signal output terminals exposed from the package for outputting the two or more device control signals; and a control circuit formed in the package, wherein the control circuit includes a circuit for outputting a device control signal to convert from an OFF state to an ON state to a device control signal output terminal in response to the ON/OFF control signal and then after a predetermined time period, outputting a device control signal to convert from an ON state to an OFF state to a device control signal output terminal.